Halogen based, and particularly fluorine based gas discharge lasers, e.g., KrF and ArF excimer lasers and molecular fluorine lasers are well known. They have been implemented in MOPA configurations, i.e., a master oscillator and a power amplifier, in which, e.g., a gas discharge laser, which is in a resonator cavity configuration, and with a very accurate line narrowing module or package (“LNM” or “LNP”) produces a seed laser beam with a precisely defined center wavelength and a bandwidth on the order of femptometers. This then is amplified in power in another (or the same) chamber by a power-amplifying laser injected with the output of the oscillator. The configuration may also be a MOPO, in which the power amplifier is also an oscillating resonator cavity. The output parameters of both the oscillator and amplifier depend on a variety of operating parameters, including the initial makeup of the gases, usually a halogen, e.g., fluorine, a noble gas, e.g., argon or krypton, and a buffer, e.g., neon. The makeup of these gasses in the oscillator and amplifier also varies over time, particularly as the halogen is consumed in the creating of the laser light output of the gas discharges occurring within the chamber containing the gasses in the oscillator or the amplifier. It has been found that previously used techniques for accounting for such things as the changes in the gas composition over time in older single chamber oscillating gas discharge lasers, i.e., without the addition of a power amplifier, are not very effective with MOPA or MOPO configurations, and especially so with the MO and PA or PO (hereinafter referred to simply as the PA) in separate chambers.
Coupling between the gas mixes in the two chambers, along with utilizations of, e.g., prior schemes, e.g., a “boost” scheme, e.g., applied to only one chamber, e.g., the PA chamber has been found to cause the gas mix to get out of balance between the MO and PA chambers.
Current F2 monitor and control unsatisfactory performance can be thought to stem primarily from at least the following two flaws:                1. Voltage accounting is adversely affected by the nonlinear voltage response to duty cycle changes as a function of current F2 concentration, that is, the voltage change due to a 75% to 6% DC change is not the same when the fill is rich versus lean; and        2. The boost logic which compensates for an excessive rise or drop in voltage currently only applies to the PA chamber, which can drive the gas mix in the two chambers out of balance.        
In the past applicants had used a so-called NewOpPoint state. The original purpose of the NewOpPoint state was to track voltage changes associated with duty cycle and energy setpoint changes. Then, only one reference voltage—plus a carefully accounted-for reference voltage offset—was originally thought to properly maintain the laser gas state. This was found in practice to provide less than acceptable performance.
The design according to preferred embodiments f the present invention set for below is intended to address the above noted flaws, with the goal of improved gas mix regulation.
A number of prior art patents and published applications address various ways of monitoring and controlling gas mix in halogen gas discharge lasers, e.g., excimer lasers and molecular fluorine lasers. U.S. Pat. No. 5,978,406, issued to Rokni, et al. on Nov. 2, 1999, entitled FLUORINE CONTROL SYSTEM FOR EXCIMER LASERS, based upon an application Ser. No. 09/016,525, filed on Jan. 30, 1998, and assigned to Cymer, related to fluorine gas replenishment at a continuous or substantially continuous rates based upon feedback from a real time or substantially real time fluorine monitor to maintain fluorine at substantially a selected value. U.S. Pat. No. 6,028,880, issued to Carlesi, et al. on Feb. 22, 2000, entitled AUTOMATIC FLUORINE CONTROL SYSTEM, based upon an application Ser. No. 09/109,596 filed on Jul. 2, 1998, which was a continuation in part of Ser. No. 09/016,525, filed on Jan. 30, 1998, now U.S. Pat. No. 5,978,406 and assigned to Cymer relates to fluorine gas replenishment at continuous or substantially continuous rates based upon feedback from a real time or substantially real time fluorine monitor, from a fluorine source at high pressure through a bottle having a volume of at least 0.3 liters, to maintain fluorine at substantially a selected value. U.S. Pat. No. 6,240,117, issued to Gong, et al. on May 29, 2001, entitled FLUORINE CONTROL SYSTEM WITH FLUORINE MONITOR, based on a application Ser. No. 09/191,446, filed on Nov. 12, 1998, which was a continuation-in-part of Ser. No. 09/016,525, filed Jan. 30, 1998 now U.S. Pat. No. 5,978,406 issued date Nov. 2, 1999 entitled FLUORINE CONTROL SYSTEM FOR EXCIMER LASER and Ser. No. 09/109,596 filed Jul. 2, 1998 now U.S. Pat. No. 6,028,880 issue date Feb. 22, 2000 entitled “Automatic Fluorine Control System” relates to an F2 replenishment system based upon the amount of fluorine found in a sample taken from “downstream of said blower” (i.e., in the chamber) measured with an absorption meter, first passing through a metal fluoride trap. U.S. Pat. No. 6,151,349, issued to Gong, et al. on Nov. 21, 2000, entitled AUTOMATIC FLUORINE CONTROL SYSTEM, and assigned to Cymer, based on an application Ser. No. 09/368,208, filed on Aug. 4, 1999, which was a CIP of an application Ser. No. 09/034,870 filed Mar. 4, 1998, now U.S. Pat. No. 6,005,879 entitled PULSE ENERGY CONTROL FOR EXCIMER LASERS relates to micro-bursts of fluorine injection comprising controlled periodic fluorine injections at intervals as low as about 3 to 5 minutes, also said to be an “almost continuous basis.” The claims are worded in such a way that continuous or substantially continuous flow of fluorine could be covered. The feedback for control is ΔE/ΔV, the change in laser output with change in charging voltage. United States Published Patent Application No. 20020186739, filed in the name of Sandstrom et al., and published on Dec. 12, 2002, entitled INJECTION SEEDED F2 LASER WITH WAVELENGTH CONTROL, and assigned to Cymer relates to adjusting laser gas pressure, buffer gas mix, F2 partial pressure to control the “centerline wavelength” of the output beam in a two chamber laser. Cymer Docket No. 2002-0070-01, inventors Ishihara, et al., filed on Nov. 27, 2002, Ser. No. 60/429,493, entitled AUTOMATIC GAS CONTROL SYSTEM FOR A TWO CHAMBER LASER, and assigned to Cymer, relates to F2 replenishment based upon the history of consumption rates over the laser life. Cymer Docket No. 2003-0001-01, inventors Rule, et al., filed on Jan. 31, 2003, Ser. No. 10/356,168, entitled AUTOMATIC GAS CONTROL SYSTEM FOR A GAS DISCHARGE LASER, and assigned to Cymer, relates to F2 replenishment based upon the history of consumption rates over the laser life. U.S. Pat. No. 6,212,214, issued to Vogler, et al. on Apr. 3, 2001, entitled PERFORMANCE CONTROL SYSTEM AND METHOD FOR GAS DISCHARGE LASERS, and assigned to Lambda Physik, relates to gas replenishment based upon the comparison of a master data set of the relationship between an output beam parameter known to vary with gas mixture status versus an input parameter and an actual data set taken during operation. U.S. Pat. No. 6,243,406, issued to Heist, et al. on Jun. 5, 2001, entitled GAS PERFORMANCE CONTROL SYSTEM FOR GAS DISCHARGE LASERS and assigned to Lamda Physik, relates to gas replenishment based upon amplified spontaneous emission (ASE) of the laser. U.S. Pat. No. 6,330,267, issued to Vogler, et al. on Dec. 11, 2001, entitled PERFORMANCE CONTROL SYSTEM AND METHOD FOR GAS DISCHARGE LASERS, and assigned to Lambda Physik, relates to halogen gas replenishment based upon the slope of an output parameter of the laser compared to an expected slope of the parameter giving an estimate of the deviation of the halogen from the optimum; and specifically claimed as the laser output versus input energy. U.S. Pat. No. 6,389,052, issued to Albrecht, et al. on May 14, 2002, entitled LASER GAS REPLENISHMENT METHOD, and assigned to Lambda Physik, relates to replenishment of gas at selected intervals with amount or the interval based on charging voltage variation to achieve output pulse power. U.S. Pat. No. 6,490,307, issued to de Mos, et al. on Dec. 3, 2002, entitled METHOD AND PROCEDURE TO AUTOMATICALLY STABILIZE EXCIMER LASER OUTPUT PARAMETERS, and assigned to Lambda Physik, relates to fluorine replenishment by inserting between 0.0001 mbar and 0.2 mbar of fluorine into the chamber at selected intervals or inserting constituent gas to increase total pressure in the chamber by a selected amount, or to increase the partial pressure of fluorine by between 0.0001 and 0.2 mbar at periodic intervals to return the fluorine gas substantially to said predetermined partial pressure; or based upon maintaining “relatively constant” laser output; or injecting fluorine at less than 5% of the amount in the chamber repeatedly to maintain relatively constant laser output; or less than 7% of the amount in the chamber at selected intervals; or less than 3% at selected intervals; or less than 0.1 mbar at selected intervals; or less than 0.05% mbar at selected intervals; or 0.02% mbar at selected intervals; or less than 10% halogen and buffer mix at selected intervals; or less than 5 mbar of halogen and buffer mix at selected intervals; or less than 2 mbar of halogen and buffer mix at selected intervals; or less than 1 mbar of halogen and buffer mix at selected intervals; and various other halogen buffer mixes of different percentages at different mbar maximums at selected intervals. U.S. Pat. No. 6,490,308, issued to Albrecht, et al. on Dec. 3, 2002, entitled LASER GAS REPLENISHMENT METHOD and assigned to Lambda Physik, relates to replenishment based on the value of the charging voltage. U.S. Pat. No. 6,493,370, issued to Albrecht, et al. on Dec. 10, 2002, entitled LASER GAS REPLENISHMENT METHOD and assigned to Lambda Physik, relates to a laser having a gas replenishment control system using a processor employing an algorithm for periodically determining gas actions for the gas supply unit to smoothly perform the gas actions which stabilize a composition of the laser gas mixture within the discharge chamber and to stabilize significant parameters of the laser beam, and in which the gas supply unit and said processor are configured to permit a quantity in a range substantially between 0.0001 mbar and 0.2 mbar of said halogen-containing constituent gas to inject into said laser tube at selected intervals, such that a degradation of the halogen-containing constituent gas is automatically compensated without substantially disturbing laser beam parameters, and also expressly claiming the gas is a halogen and the processor also controls discharge voltage based at least in part on energy information received from an energy detector; and also expressly claiming the control is based on discharge voltage variation necessary for a predetermined output energy. U.S. Pat. No. 6,504,861, issued to Albrecht, et al. on Jan. 7, 2003, entitled LASER GAS REPLENISHMENT METHOD, assigned to Lambda Physik, relates to replenishment periodically between a certain range of mbar of a gas, based upon a known amount injected in a prior replenishment which amount injected in the prior replenishment was based on a known amount of the gas in the chamber prior to the last injection; and also claimed is varying the intervals based on the same criteria. U.S. Pat. No. 6,529,533, issued to Voss on Mar. 4, 2003, entitled BEAM PARAMETER MONITORING UNIT FOR A MOLECULAR FLUORINE (F2) LASER, assigned to Lambda Physik, relates to a molecular fluorine laser with fluorine replenishment based upon detected value of at least one of energy, energy stability, bandwidth, wavelength, beam profile, pulse shape, pulse duration, output power, pulse length and pulse to pulse stability relating to the UV beam, the red beam having been separated from the UV beam. U.S. Pat. No. 6,563,853, issued to Heist, et al. on May 13, 2003, entitled GAS PERFORMANCE CONTROL SYSTEM FOR GAS DISCHARGE LASERS, and assigned to Lambda Physik, relates to gas replenishment based upon a sample of the amplified spontaneous emission (ASE) output of the laser. United States Published Patent Application No. 20010012309 filed in the name of Albrecht, et al. and published on Aug. 9, 2001, entitled LASER GAS REPLENISHMENT METHOD, and assigned to Lambda Physik, relates to gas replenishment with the amount at selected intervals of the intervals chosen based on the charging voltage; or also claimed based on the amount injected in a previous injection. United States Published Patent Application No. 20020101901, filed in the name of Albrecht, et al. and published on Aug. 1, 2002, entitled LASER GAS REPLENISHMENT METHOD, and assigned to Lambda Physik, relates to a laser gas replenishment at periodic intervals from within a pre-selected range with the amount from within the range or the interval selected based upon a calculated amount of replenishment in the last replenishment. United States Published Patent Application No. 20020101902, filed in the name of Albrecht, et al. and published on Aug. 1, 2002, entitled Laser gas replenishment method and assigned to Lambda Physik, relates to laser gas replenishment utilizing a processor based upon charging voltage. United States Published Patent Application No. 20020110174, filed in the name of Albrecht, et al., and published on Aug. 15, 2002, entitled LASER GAS REPLENISHMENT METHOD, and assigned to Lambda Physik, relates to halogen gas replenishment of less that 0.2 mbar, or halogen constituent gas at less than 7% of current chamber content, at regularly selected intervals, or also claimed at same limits with replenishment interval based on charging voltage. U.S. Pat. No. 5,142,543, issued to Wakabayashi, et al. on Aug. 25, 1992, entitled METHOD AND SYSTEM FOR CONTROLLING NARROW-BAND OSCILLATION EXCIMER LASER, assigned to Komatsu, relates to gas replenishment based upon the charging voltage. U.S. Pat. No. 5,450,436 issued to Mizoguchi, et al. on Sep. 12, 1995, entitled LASER GAS REPLENISHING APPARATUS AND METHOD IN EXCIMER LASER SYSTEM, and assigned to Komatsu, relates to halogen gas replenishment based upon beam width and with periodic injection, i.e., with a predetermined amount varied up or down based on beam width; or alternatively claimed to inject a halogen constituent gas at predetermined intervals to a level that maintains total pressure and stopping the exhaust while injecting; or alternatively claimed injecting a predetermined amount after a predetermined number of pulses; or alternatively based on accumulated pulses and pulse rate; or alternatively claimed as replenishing the halogen on one pulse count and the rare gas on another and exhausting to maintain pressure; or alternatively claimed as replenishing the halogen based on pulse count and the rare gas based on charging voltage. U.S. Pat. No. 5,642,374, issued to Wakabayashi, et al. on Jun. 24, 1997, entitled EXCIMER LASER DEVICE, and assigned to Komatsu, relates to gas replenishment based upon laser output beam bandwidth. U.S. Pat. No. 5,754,579, issued to Mizoguchi, et al. on May 19, 1998, entitled LASER GAS CONTROLLER AND CHARGING/DISCHARGING DEVICE FOR DISCHARGE-EXCITED LASER, and assigned to Komatsu, relates to gas replenishment/exhaust based upon output of laser or alternatively claimed as based upon the charging voltage; including separately claimed based upon bandwidth. U.S. Pat. No. 6,130,904, issued to Ishihara, et al. on Oct. 10, 2000, entitled GAS SUPPLEMENTATION METHOD OF EXCIMER LASER APPARATUS, and assigned to Komatsu, relates to halogen gas replenishment based upon partial pressure; or alternatively claimed as based on band width; or alternatively claims supplementation of a mix of rare gas and buffer gas based upon a calculated oscillation stop time; or alternatively based upon a number of other possible parameters, including based upon laser output; or alternatively claimed as based upon a “power lock voltage”; or alternatively based upon the charging voltage; or alternatively based upon a pulse count.
Japanese Patent No. 2601410, the Published Application of which (08008481 was published on Jan. 12, 1996 (application 06134468 filed on Jun. 16, 1994), assigned to Komatsu (corresponding to U.S. Pat. No. 5,754,579, which claims priority from this application and another), refers to gas replenishment based on charging voltage or beam width and charging voltage. Japanese Patent No. 2701184, the Published Application of which (05192555 JP) was published on Apr. 23, 1993 (application 03290618 filed on Oct. 9, 1991), assigned to Komatsu, refers to controlling the mixture of the constituent gas mixture, based upon pulse count. Japanese Patent No. 3297108, issued on Jul. 2, 2002, assigned to Komatsu (U.S. Pat. No. 5,450,436 claims priority from this application and others), refers to gas replenishment after selected pulse count and replenishment to maintain chamber gas pressure. Claims, roughly translated refer to injection of rare gas based upon exhaust volume (“swept volume”). Japanese Published Patent Application No. 10074993 JP, published on Mar. 1, 1998, entitled GAS LASER AND LASER GAS INJECTION METHOD (Application 08246821, filed on Aug. 30, 1996) refers to gas replenishment with injections based upon chamber pressure. Japanese Patent Application No. 2001332793, published on Nov. 30, 2001 (Application JP 2000150874, filed on May 23, 2000), assigned to Komatsu, relates to feedback control, possibly including gas replenishment, based on beam properties. Japanese Published Patent Application No. 2002208746, published on Jul. 26, 2002 (Application JP 20011214 filed on Jan. 9, 2001), assigned to Komatsu, refers to replenishment based on a ratio of gases in the mixture in the chamber. Japanese Published Patent Application 10074993 JP, published on Mar. 1, 1998, based on Japanese application 08246821, filed on Aug. 30, 1996, by Wakabayashi, et al., entitled GAS LASER AND LASER GAS INJECTION METHOD, assigned to Komatsu (GigaPhoton), refers to a filtered replenishment based on chamber pressure. Japanese Published Patent Application No. 20020294856, published on Oct. 20, 2001 (Application JP 99272496, filed on Sep. 27, 1999), relates to replenishment of Xenon based upon Xe content apparently in the chamber. Japanese Published Patent Application No. 09097951 JP, published on Apr. 1, 1997, based on a Japanese Patent Application No. 07289105, filed on Sep. 29, 1995 by Senrin, et al., entitled EXCIMER LASER APPARATUS, and assigned to Nissin Electric, refers to replenishment based upon charging voltage. Japanese Published Patent application No. 2000022255, published on Jan. 21, 2000, with inventors Omi, et al., entitled METHOD FOR STABILIZING AND CONTROLLING FLUORINE GAS CONCENTRATION AND CONTROL MECHANISM THEREOF, based on a Japanese Patent Application No. JP19980191178, filed on Jul. 7, 1998 and assigned to Horiba, refers to measuring in real time the content of fluorine in the “mixed gas” by measuring absorption of UV light in the “mixed gas” and creating a feedback control signal to correct any excess or deficiency against a set value. The disclosures of all of the above are hereby incorporated by reference.